Nitrogen Atmosphere Diffusion Bonding for Stainless Steel
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Solution Overview
Problem
Existing diffusion bonding methods face challenges in ensuring bonding strength, particularly with nitrogen doped stainless steel materials, due to oxide film formation, high equipment costs, and difficulty in completely removing oxygen from the bonding environment, leading to increased processing costs and potential corrosion resistance issues.
Innovation Solution
A bonding method using a nitrogen gas atmosphere within a controlled pressure range of 3-105 Pa to prevent oxide film formation, eliminating the need for high vacuum evacuation mechanisms and expensive inert gases, while allowing nitrogen to enter into a solid solution, enhancing joint strength and corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high vacuum evacuation is performed using rotary pump and diffusing pump to prevent oxide film formation, then bonding strength is improved, but equipment cost increases significantly
Solution Approach 1:
The patent uses a nitrogen gas atmosphere instead of high vacuum to prevent oxide film formation during diffusion bonding. The nitrogen atmosphere provides an oxygen-free environment that protects the metallic bonding objects from oxidation, while eliminating the need for expensive diffusing pumps and high vacuum evacuation systems.
2Strength
If inert gas atmosphere (argon, helium) is used to prevent oxide film formation, then bonding strength is improved, but processing cost increases due to high gas cost and incomplete oxygen removal
Solution Approach 1:
The patent replaces expensive inert gases (argon, helium) with nitrogen gas, which is significantly cheaper and more readily available. The nitrogen atmosphere provides sufficient protection against oxide film formation without the high cost associated with noble gases, making the diffusion bonding process economically viable.
3Device complexity
If nitrogen gas is introduced at atmospheric pressure for diffusion bonding, then equipment cost is reduced, but oxide film formation occurs reducing bonding strength
Solution Approach 1:
The patent optimizes the nitrogen gas pressure to a specific range (1-1000 Pa, preferably 1-100 Pa) to simultaneously achieve oxide film prevention and cost reduction. This pressure parameter change creates the right balance between maintaining an oxygen-free environment and avoiding the need for expensive high vacuum equipment.
4Strength
If melt welding is performed on nitrogen doped stainless steel, then joining is achieved, but nitrogen content at bonding region decreases reducing corrosion resistance
Solution Approach 1:
The patent replaces melt welding with diffusion bonding, a solid-state joining process that occurs below the melting point of the materials. This substitution prevents nitrogen loss and maintains the nitrogen content in the bonding region, thereby preserving the corrosion resistance of nitrogen doped stainless steel while achieving strong joints.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively prevents oxide film generation, reduces equipment and processing costs, and ensures strong, corrosion-resistant bonds by promoting efficient diffusion bonding without the need for high-cost pumps or inert gases.
Implementation Method 1
when oxygen is included excessively within the bonding environment, an oxide film is formed on the surface of the metallic bonding objects... By controlling the pressure inside the bonding vessel to be between 3-105 Pa while introducing nitrogen gas, oxide film formation is prevented
Implementation Method 2
by carrying out electrical energization or high frequency heating or the like, while pressure is imparted to bonding objects that are in mutual contact with each other, the objects are heated whereupon atoms existing at the contact region are dispersed, and as a result, both of the bonding objects are joined (bonded) together
Implementation Method 3
while pressure is imparted to bonding objects that are in mutual contact with each other, the objects are heated whereupon atoms existing at the contact region are dispersed
Implementation Method 4
by carrying out electrical energization or high frequency heating or the like, while pressure is imparted to bonding objects that are in mutual contact with each other, the objects are heated
Implementation Method 5
nitrogen to enter into a solid solution, enhancing joint strength and corrosion resistance
Data Source
AI summary
A nitrogen gas tank, a rotary pump and a mechanical booster pump are connected to a bonding vessel that constitutes a bonding apparatus for carrying out diffusion bonding, the apparatus further comprising a pressure sensor. A nitrogen gas atmosphere is formed inside the bonding vessel, and under control operations of a control circuit, a nitrogen introduction rate is controlled so that a pressure is substantially fixed at a predetermined pressure between 3-105 Pa. At such a state, under the action of a rod of a hydraulic cylinder, a second electrode is brought into proximity with a first electrode, so that ultimately, a first object to be bonded and a second object to be bonded on the first electrode are pressed. Further, current is applied through the first electrode and the second electrode with respect to the first object to be bonded and the second object to be bonded.